1. Field of the Invention
The present invention pertains to methods of achieving transmitter frequency lock between nodes in a full duplex communications link.
2. Art Background
A full duplex link consists of two transmitter/receiver nodes, using two frequencies. Typical designs make use of a reference oscillator for each transmitter and receiver, four total. The two operating frequencies are typically offset by a fixed amount. When operating radio links at millimeter wavelengths, for example in the neighborhood of 60 Giga Hertz (GHz), phase locked loop (PLL) techniques commonly used at lower frequencies that allow one reference to be derived from the other are impractical. For example, using frequencies of 60 and 62.5 GHz, stable dividers which will work over a wide temperature range are difficult to make. Intermediate frequency (IF) PLL designs which will hand/e large bandwidth (on the order of 1.5 GHz) require IF frequencies high enough so that they interfere with received signals.
What is needed is a way of achieving frequency lock in a duplex link which does not require separate reference oscillators for both transmitter and receiver.